DESCRIPTION: (Adapted from abstract). The long-term goal of Dr. Laird's laboratory is to determine the role of DNA methylation in cancer. 5-Methylcytosine DNA methylation can mediate epigenetic effects through alterations in gene expression as well as genetic effects through an increased mutation rate of 5-methylcytosine. Dr. Laird recently showed that polyp formation in the ApcMin/+mouse model could be almost completely prevented by lowering the levels of functional DNA methyltransferase (MTase) expression and thus the levels of DNA methylation. The goal of the proposed study is to elucidate the mechanism by which reduced DNA MTase levels suppress intestinal polyp formation in ApcMin/+ mice. There are four specific aims. 1) Determine whether the tumor-suppressive effect of DNA hypomethylation is restricted to intestinal neoplasia or whether it is a general characteristic of ApcMin/+ -induced tumors. He will address this by determining the effect of DNA hypomethylation of ApcMin/+ -induced tumors in the pancreas. 2) Test the hypothesis that DNA hypomethylation suppresses polyp formation by reducing the frequency of 5-methylcytosine mutation events. He will test this hypothesis using mutation assays in tissue culture and in vivo. 3) Test the hypothesis that lower levels of DNA MTase impair DNA hypermethylation of tumor-suppressor genes. He will use a novel quantitative assay to track CpG island hypermethylation in microdissected normal epithelium and adenomas from mice with different levels of DNA MTase. 4) Test the hypothesis that DNA hypomethylation suppresses intestinal polyp formation by decreasing the rate of loss of heterozygosity of the Apc gene. He proposes to use a tissue culture selection assay to determine the effect of DNA methylation on chromosome stability.